Stationary vane and centrifugal compressor provided with stationary vane

ABSTRACT

A stationary vane includes: a side surface exposed to a fluid and that is provided along a flow direction of the fluid; and corner portions provided in the side surface and that generates, at a downstream side in the flow direction of the fluid, streamwise vortexes each having a vortex axis that is parallel to the flow direction of the fluid.

TECHNICAL FIELD

The present invention relates to a stationary vane to be provided to a fluid machine and a centrifugal compressor provided with the stationary vane.

BACKGROUND

The fluid machine exchanges energy between fluid and the machine. For example, a centrifugal compressor, which is a fluid machine (driven machine), is capable of pumping (compressing) fluid, using centrifugal force by the impeller rotating together with the rotating shaft.

In a fluid machine such as the centrifugal compressor described above, various stationary vanes provided in the flow path where fluid flows improve the flow of fluid and thus improve the efficiency of the energy exchange. Examples of stationary vanes to be provided to centrifugal compressors include diffuser vanes disposed downstream of the impeller in the flow direction (see Patent Document 1) and return vanes.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Utility Model Registration Application Publication No. Hei 1-174599

However, the stationary vanes provided in the flow path cause partial irregularities of the fluid in the vicinities of the stationary vanes while improving the overall flow of the fluid in the flow path. Here, the flow of fluid at the trailing edge of a stationary vane (the downstream edge in the flow direction of the fluid) and in the vicinity thereof in a fluid machine is illustrated in FIG. 6.

As illustrated in FIG. 6, although fluid G₁ flows well along a stationary vane 150, fluid G₂, a part of the fluid, separates from surfaces 151 and 153 of the stationary vane 150, and in addition, fluid G₃, a part of the fluid, flows being swirled into the space downstream of the stationary vane 150 in the flow direction (on the lower side in FIG. 6), which generates transverse vortexes 190. The separation of the fluid and the generation of the transverse vortexes as described above are fluid loss and affect the efficiency of the fluid machine.

In order to suppress the separation of the fluid and the generation of the transverse vortexes, the cross-sectional shape of a trailing edge 150 a of the stationary vane 150 is sometimes formed to be in an arc shape S or the like (see the chain double-dashed line in FIG. 6). Such a cross-sectional shape of the trailing edge 150 a of the stationary vane 150 can suppress the separation of the fluid and the generation of the transverse vortexes to some extent, but it cannot sufficiently suppress the separation of the fluid and the generation of the transverse vortexes in the case where the speed of the fluid G₁ (flow speed) flowing along the stationary vane 150 is high or the case where the direction of the flow of the fluid G₁ is changed sharply by the stationary vane 150.

SUMMARY

One or more embodiments of the invention reduce fluid loss at the stationary vanes and improve the efficiency of the fluid machine.

One or more embodiments of the invention are directed to a stationary vane provided to a fluid machine, characterized in that the stationary vane includes: a side surface to be exposed to fluid, the side surface being formed along a flow direction of the fluid; and a corner formed on the side surface, the corner being capable of generating a streamwise vortex having a vortex axis extending along the flow direction of the fluid, on a downstream side in the flow direction of the fluid.

One or more embodiments of the invention are directed to a stationary vane, characterized in that the corner is formed by a ditch recessed from the side surface.

One or more embodiments of the invention are directed to a stationary vane, characterized in that a plurality of the ditches are formed on the side surface so as to be arranged in a direction intersecting the flow direction of the fluid, and the ditches have different shapes depending on a speed of the fluid flowing along the side surface in a vicinity of each ditch.

One or more embodiments of the invention are directed to a centrifugal compressor that includes: a casing, a rotating shaft rotatably supported by the casing, an impeller which is provided to the rotating shaft and is rotationally driven together with the rotating shaft, and a flow path which is formed in the casing and houses the impeller, the centrifugal compressor being configured to compress fluid by passing the fluid through the flow path, characterized in that the centrifugal compressor comprises the stationary vane according to one or more embodiments of the invention in the flow path.

According to one or more embodiments of the invention, the corner formed on the side surface generates a streamwise vortex on the downstream side of the stationary vane in the flow direction, and the streamwise vortex draws the fluid flowing along the side surface of the stationary vane, which suppresses the separation of the fluid from the side surface. In addition, the streamwise vortex generated downstream of the stationary vane in the flow direction interferes with the transverse vortex similarly generated downstream of the stationary vane in the flow direction, and thus can break the transverse vortex. As above, the generation of the streamwise vortex suppresses the separation of the fluid and breaks the transverse vortex, which reduces the fluid loss at the stationary vane and improves the efficiency of the fluid machine.

According to one or more embodiments of the invention, the stationary vane makes it possible to form the corner on the side surface with a simple configuration.

According to one or more embodiments of the invention, by forming each of the ditches to be in a shape in accordance with the flow speed of the fluid flowing along the side surface, it is possible to suppress turbulent flows and other irregularities of the fluid and uniform the strengths of the generated streamwise vortexes.

According to one or more embodiments of the invention, the centrifugal compressor makes it possible to reduce fluid loss in other stationary vanes such as struts, inlet guide vanes, diffuser vanes, and the like in a centrifugal compressor which compresses fluid using centrifugal force by the impeller rotating together with the rotating shaft, and improve the efficiency of the centrifugal compressor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal cross-sectional view illustrating a schematic structure of a centrifugal compressor including return vanes according to one or more embodiments of the invention.

FIG. 2 is an explanatory diagram illustrating arrangement of the return vanes according to one or more embodiments of the invention in a return flow path (a cross-sectional view seen from arrows II-II in FIG. 1).

FIG. 3A is a schematic perspective view illustrating a trailing edge of the return vane according to one or more embodiments of the invention.

FIG. 3B is a schematic perspective view illustrating an example in which the number of ditches and other factors at the trailing edge of the return vane according to one or more embodiments of the invention is changed.

FIG. 4A is an explanatory diagram illustrating the trailing edge of the return vane according to one or more embodiments of the invention (a view seen from arrow IV in FIG. 3A).

FIG. 4B is an explanatory diagram illustrating an example in which the shape of the ditches at the trailing edge of the return vane according to one or more embodiments of the invention is changed.

FIG. 4C is an explanatory diagram illustrating an example in which the shape of the ditches at the trailing edge of the return vane according to one or more embodiments of the invention is changed.

FIG. 4D is an explanatory diagram illustrating an example in which ditches at the trailing edge of the return vane according to one or more embodiments of the invention are changed to protrusions.

FIG. 5A is an explanatory diagram illustrating the trailing edge of the return vane according to one or more embodiments of the invention (a cross-sectional view seen from arrows V-V in FIG. 3A).

FIG. 5B is an explanatory diagram illustrating an example in which the shape of the trailing edge of the return vane according to one or more embodiments of the invention is changed.

FIG. 5C is an explanatory diagram illustrating an example in which the shape of the trailing edge of the return vane according to one or more embodiments of the invention is changed.

FIG. 6 is an explanatory diagram illustrating the flow of fluid at the trailing edge of a stationary vane and in the vicinity thereof in a conventional fluid machine.

DETAILED DESCRIPTION

Hereinafter, embodiments of a stationary vane will be described in detail with reference to the attached drawings. Note that the following embodiments employs the stationary vane in return vanes provided in a multistage centrifugal compressor.

As a matter of course, the present invention is not limited to the following embodiments. Embodiments of the present invention may be adopted to other stationary vanes in centrifugal compressors, such as struts, inlet guide vanes, and diffuser guide vanes, or may be adopted to various stationary vanes provided in other fluid machines, such as turbochargers and pumps. In addition, it goes without saying that various modifications can be made without departing from the spirit of the embodiments of the present invention.

Descriptions will be provided for the structure of a centrifugal compressor including return vanes according to one or more embodiments of the present invention with reference to FIGS. 1, 2, 3A and 4A.

As illustrated in FIG. 1, a centrifugal compressor (fluid machine) 1 is provided with a casing 11 in a substantially cylindrical shape. The casing 11 rotatably supports a rotating shaft 12 via bearings 13. The rotating shaft 12 is connected to a non-illustrated drive source, such as a motor, and configured to rotate in the casing 11 when the drive source is driven. Note that FIG. 1 illustrates only a half of the centrifugal compressor 1 (the upper half in FIG. 1).

The casing 11 has a suction port 21 for taking fluid G into the centrifugal compressor 1 and a discharge port 22 for discharging the fluid G to the outside of the centrifugal compressor 1. Formed inside the centrifugal compressor 1 is a flow path 30 connecting the suction port 21 and the discharge port 22, for sending the fluid G in one axis direction (from the left side to the right side in FIG. 1).

The flow path 30 is defined by first side walls 11 a, second side walls 11 b, and other portions and formed such that the diameter thereof repeatedly decreases and increases. Here, a plurality of the first side walls 11 a are provided on the radially inside of the flow path 30 (on the lower side in FIG. 1) along the axial direction (the right-left direction in FIG. 1) at intervals, and a plurality of the second side walls 11 b are provided between the first side walls 11 a so as to extend (protrude) radially inward from the radially outer side (the upper side in FIG. 1).

The flow path 30 includes compression flow paths 31 for compressing (pumping) the fluid G, diffuser flow paths 32 for decelerating the fluid G pumped from the compression flow paths 31 to convert the dynamic pressure to the static pressure, and return flow paths 33 for eliminating turning components in the flow of the fluid G sent from the diffuser flow paths 32 and sending the fluid G to the compression flow path 31 in the next stage.

The centrifugal compressor 1 includes multiple stages of the compression flow path 31, diffuser flow path 32, and return flow path 33 sequentially provided along the flow direction of the fluid G, and the fluid G is compressed in stages in the course of flowing the flow path 30 from the suction port 21 toward the discharge port 22.

The compression flow path 31 is formed to gradually curve radially outward, toward the axially rear end side (the right end side in FIG. 1) from the axially front end side (the left end side in FIG. 1), and the compression flow path 31 houses impellers 40. The impellers 40 are fixed to the rotating shaft 12 and rotate together with the rotating shaft 12 when the non-illustrated drive source is driven.

Accordingly, in the compression flow path 31, the fluid G taken in from the suction port 21 or the fluid G sent from the compression flow path 31 in the previous stage is given a centrifugal force directed radially outward (in a direction orthogonal to the rotating shaft 12) by the impeller 40 rotating together with the rotating shaft 12, and sent (pumped) to the diffuser flow path 32 located immediately downstream in the flow direction (radially outward).

The diffuser flow path 32 is formed in an annular shape extending radially outward from the compression flow path 31 located immediately upstream thereof in the flow direction (radially inward). In the diffuser flow path 32, the fluid G sent from compression flow path 31 is diffused radially outward and at the same time, sent to the return flow path 33 located immediately downstream thereof in the flow direction (radially outward and axially rearward). Note that by the fluid G being diffused in the diffuser flow path 32, the flow speed thereof is reduced (decelerated), and at the same time, the kinetic energy (dynamic pressure) given to the fluid G is converted into pressure energy (static pressure).

The return flow path 33 is formed to connect the diffuser flow path 32 located immediately upstream thereof in the flow direction (on the axially front end side and radially inward) and the compression flow path 31 located immediately downstream thereof in the flow direction (on the axially rear end side), in an annular shape extending in the radial direction and the axial direction such that the longitudinal section thereof forms a letter U. Provided in the return flow path 33 is a return vane 50 circumferentially partitioning a part of the space in the return flow path 33.

The return vanes 50 are plate-like members provided to connect the first side walls 11 a and the second side walls 11 b in the casing 11 (see FIGS. 1, 3A, and 4A), each having a shape circumferentially curving, and are arranged radially, spaced at certain intervals in the circumferential direction (see FIG. 2). Thus, the fluid G is sent from the diffuser flow path 32, and the flow direction is inverted radially inward. Then, in the return flow path 33, the fluid G is flowed toward the impeller 40 (compression flow path 31) in the next stage, and at the same time, turning components in the flow of the fluid G are eliminated (cancelled) by the return vane 50 (see FIGS. 1 and 2).

As illustrated in FIG. 3A, each return vane 50 has ditches 60 formed on (are open on) a side surface 51 and a rear end surface 52. Here, the side surface 51 is one surface (a suction surface) exposed to the fluid G and extending along the flow direction of the fluid G, and the rear end surface 52 is an end surface on the downstream side in the flow direction of the fluid G. Note that FIG. 3A only illustrates the return vane 50, and the casing 11 (the first side wall 11 a and the second side wall 11 b) is not illustrated for the figure to be easier to understand.

Each ditch 60 has a grooved surface 61 recessed from the side surface 51 of the return vane 50, and at a trailing edge (edge on the downstream side in the flow direction) 50 a of the return vane 50, the side surface 51 and the grooved surface 61 form corners 70 protruding in a direction intersecting the flow direction. The shapes of the ditch 60 and the corner 70 will be described later.

Thus, the flow direction of the fluid G flowing along the side surface 51 of the return vane 50 changes at the trailing edge 50 a of the return vane 50 such that the fluid G is swirled by the ditches 60 (grooved surfaces 61). As a result, streamwise vortexes 80 of the fluid G are generated downstream of the return vane 50 in the flow direction.

The streamwise vortexes 80 each have a vortex axis C₈₀ in parallel with the flow direction of the fluid G and are generated downstream of the return vane 50 in the flow direction (along extended lines of the side surface 51) starting from the corners 70. Accordingly, the fluid G flows so as to be drawn (swirled) into the streamwise vortexes 80 after flowing along the side surface 51 of the return vane 50, which suppresses the separation of the fluid G from the side surface 51.

In addition, the streamwise vortexes 80 generated downstream of the return vane 50 in the flow direction interfere with transverse vortexes 90 similarly generated downstream of the return vane 50 in the flow direction. Here, the transverse vortexes 90 are vortexes (for example, a Karman vortex street) each having a vortex axis C₉₀ orthogonal to (intersecting) the flow direction. These streamwise vortexes 80 and transverse vortexes 90 interfere with and cancel (break) each other. More specifically, the transverse vortexes 90, which greatly affect the flow performance of the fluid G in conventional apparatuses, are broken by the generation of the streamwise vortexes 80, which consequently reduces the fluid loss at the return vane 50 and improves the efficiency of the centrifugal compressor 1.

The shapes of the ditch 60 and the corner 70 will be described in detail with reference to FIGS. 3A to 5C.

As illustrated in FIGS. 3A and 4A, the return vane 50 has two ditches 60, which are formed to be spaced with a certain distance (ditch interval a) in between so as to be arranged symmetrically in the vane width direction of the return vane 50 (the direction in which the trailing edge 50 a extends and the up-down direction in FIG. 4A).

Accordingly, the trailing edge 50 a of the return vane 50 has four corners 70 formed by the side surface 51 and the two grooved surfaces 61. Consequently, four streamwise vortexes 80, each starting from one of the four corners 70, are generated downstream of the return vane 50 in the flow direction (see FIG. 3A). As a matter of course, the number of ditches 60 formed on the return vane 50 is not limited to that in these embodiments, but one or more ditches 60 may be formed on the return vane 50.

Here, in the case where one ditch 60 is formed on the return vane 50, it is preferable that the ditch 60 be arranged substantially at the center in the vane width direction of the return vane 50 (not illustrated). By arranging the one ditch 60 substantially at the center in the vane width direction of the return vane 50 as above, the corners 70 formed by the side surface 51 of the return vane 50 and the grooved surface 61 of the ditch 60 are arranged substantially uniformly (symmetrically) in the vane width direction of the return vane 50. Note that in this case, the length of the ditch 60 (ditch width W) in the vane width direction of the return vane 50 is the distance between both corners 70 formed by the side surface 51 and the grooved surface 61.

In the case where multiple ditches 60 are formed on the return vane 50, it is preferable that the multiple ditches 60 be spaced at certain intervals (ditch interval a) and arranged symmetrically in the vane width direction of the return vane 50 (see FIG. 4A). In this case, it is preferred that the length of the ditch 60 (ditch width W) in the vane width direction of the return vane 50 and the distance between the ditches 60 (ditch interval a) in the vane width direction of the return vane 50 be substantially the same length (distance) (see the following Formula (1)).

[Math.1]

0.9<a/W<1.1   (1)

By spacing the multiple ditches 60 as described in Formula (1) as above and by arranging them symmetrically in the vane width direction of the return vane 50, the corners 70 formed by the side surface 51 of the return vane 50 and the grooved surfaces 61 of the ditches 60 are arranged substantially uniformly (symmetrically) in the vane width direction of the return vane 50. Note that in this case, the length of the ditch 60 (ditch width W) in the vane width direction of the return vane 50 is the distance between both corners 70 formed by the side surface 51 and the grooved surface 61, and the distance between the ditches 60 (ditch interval a) in the vane width direction of the return vane 50 is the distance between the corners 70 of two adjacent ditches 60.

As described above, in the case where one or more ditches 60 are formed on the return vane 50, by arranging the corners 70 substantially uniformly (symmetrically) in the vane width direction of the return vane 50, the amount of flow of the fluid G contributing to the generation of the streamwise vortexes 80 starting the corners 70 is substantially uniform, and the strengths of the streamwise vortexes 80 generated downstream of the return vane 50 in the flow direction are uniform (see FIG. 3A). In addition, for the fluid G flowing along the side surface 51 of the return vane 50, multiple (four in FIG. 3A) streamwise vortexes 80 are generated substantially uniformly (symmetrically) in the vane width direction of the return vane 50, which suppresses the separation of the fluid G substantially uniformly in the vane width direction of the return vane 50.

In addition, in the case where multiple ditches 60 are formed on the return vane 50, the lengths of the ditches 60 (ditch depth H) in the vane thickness direction of the return vane 50 (the thickness direction of the trailing edge 50 a and the right-left direction in FIG. 5A) and the lengths of the ditches 60 (ditch length L) in the vane length direction of the return vane 50 (the flow direction and the up-down direction in FIG. 5A) may be set individually (independently) (see FIGS. 3A and 5A). For example, multiple ditches 60 may have different ditch lengths L while having the same ditch depth H, or multiple ditches 60 may have different ditch depths H while having the same ditch length L. Alternatively, multiple ditches 60 may have different ditch depths H and different ditch lengths L such that the ratio between the ditch depth H and the ditch length L is the same or different.

In this case, it is preferable that the ditch depths H and the ditch lengths L of multiple ditches 60 be set to be a relatively changed value depending on the flow speed distribution of the fluid G flowing along the side surface 51 of the return vane 50. This is because the flow speed of the fluid G flowing along the return vane 50 is different depending on the position where the fluid G flows. Hence, depending on the position (arrangement location) of each ditch 60 formed on the return vane 50, the ditch depth H and the ditch length L are set to be a relatively changed value.

As illustrated in FIG. 3A, in the case where two ditches 60 are formed on the return vane 50, the two ditches 60 are arranged to be symmetrical to each other in the vane width direction of the return vane, and there are streams of fluid G having the same flow speed in the peripheries of both ditches 60. Accordingly, the ditch depths H and the ditch lengths L of both ditches 60 are set to the same values.

On the other hand, as illustrated in FIG. 3B, in the case where three ditches 60-1 and 60-2 are formed on the return vane 50, the three ditches 60-1 and 60-2 are arranged, one at the center in the vane width direction of the return vane 50 and two symmetrically on both sides thereof (on the upper side and the lower side in FIG. 3B), and there are streams of the fluid G₁ and G₂ having different flow speeds in the peripheries of the ditches 60-1 and 60-2. Accordingly, the ditch depths H and the ditch lengths L₁ and L₂ of the ditches 60-1 and 60-2 are set in accordance with the speeds of the streams of the fluid G₁ and G₂ flowing in the peripheries of the ditches 60-1 and 60-2.

For example, as illustrated in FIG. 3B, the ditch depths H of the ditches 60-1 and 60-2 are set to be equal (to the same value) while the ditch length L₁ of the ditch 60-1 formed at the center in the vane width direction of the return vane 50, where the fluid G₁ with a high flow speed flows, is set longer than the ditch length L₂ of the ditches 60-2 formed on both sides in the vane width direction of the return vane 50, where the fluid G₂ with a lower flow speed than that at the center flows.

By setting the ditch depth H and the ditch lengths L₁ and L₂ of the multiple ditches 60-1 and 60-2 as above, the fluid G₁ with a high flow speed flows on the grooved surface 61-1, which is long in the flow direction and has a gentle inclination, at the center of the return vane 50, and thus separation, turbulent flows, or other irregularities are unlikely to occur. On both sides thereof, the fluid G₂ with a slow flow speed flows on the grooved surfaces 61-2, which are short in the flow direction and have a steep inclination, generating streamwise vortexes 80 strong enough to prevent separation, turbulent flows, or other irregularities.

Note that as illustrated in FIG. 5A, when the ditch depth H of the ditch 60 is set, it is set to be smaller than the vane thickness T so that the ditch 60 does not pass through the trailing edge 50 a of the return vane 50 (see the following Formula (2)).

[Math.2]

H<T   (2)

By forming the ditches 60 on the return vane 50 as expressed by Formula (2) as above, the fluid G flowing along the side surface 51 of the return vane 50 will not flow into the opposite side surface (pressure surface) 53 side of the return vane 50. Accordingly, the fluid G flows being swirled by the ditch 60, generating the streamwise vortexes 80 downstream of the return vane 50 in the flow direction (on the lower side in FIG. 5A) starting from the corners 70.

Note that the vane thickness T is the width of the rear end surface 52 of the return vane 50 in the case where the cross-sectional shape of the trailing edge 50 a is rectangular (see FIG. 5A). In the case where the cross-sectional shape of the trailing edge 50 a is circular, the vane thickness T is the maximum width of the portion where the arc Sc is tangent to the outer shape of the return vane 50 (see FIG. 5B). In the case where the cross-sectional shape of the trailing edge 50 a is elliptical, the vane thickness T is the maximum width of the portion where the ellipse Se is tangent to the outer shape of the return vane 50 (see FIG. 5C).

As illustrated in FIGS. 3A and 4A, the corners 70 are formed by the side surface 51 of the return vane 50 and the grooved surface 61 of the ditch 60, and the grooved surface 61 is a curved surface recessed into a curved shape from the side surface 51. As a matter of course, the corner 70 and the grooved surface 61 (ditch 60) are not limited to these embodiments, but may be of various shapes.

The ditch 60 forming the corners 70 may be, for example, a ditch 60 formed by a grooved surface 61 grooved in to a rectangular shape from the side surface 51 of the return vane 50 (see FIG. 4B), or a ditch 60 formed by a grooved surface 61 recessed in to a wedge shape from the side surface 51 of the return vane 50 (see FIG. 4C).

In addition, the corners 70 maybe formed by, for example, protrusions 62 formed by protruded surfaces 63 protruding from the side surface 51 of the return vane 50 (see FIG. 4D). In this case, the vicinity of the protrusion 62 may be flush with the side surface 51 of the return vane 50, or it may be a grooved surface 61 recessed from the side surface 51 of the return vane 50 as indicated by chain double-dashed lines in FIG. 4D.

By forming the grooved surface 61 recessed from the side surface 51 of the return vane 50 in the vicinity of the protrusion 62 as above, it is possible to increase the length of the protrusions 62 (protrusion heights H₁ and H₂) in the vane thickness direction (right-left direction in FIG. 4D) of the return vane 50 (H₁<H₂), and thus possible to strengthen the streamwise vortexes 80 generated downstream of the return vane 50 in the flow direction.

With any foregoing shape illustrated in FIGS. 4A to 4D, when the fluid G flowing along the side surface 51 reaches the trailing edge 50 a of the return vane 50, the streamwise vortexes 80 of the fluid are formed starting from the corners 70 formed by providing the ditches 60 or the protrusions 62, which suppresses the separation of the fluid G from the return vane 50 (side surface 51) and also cancels the transverse vortexes 90 generated downstream of the return vane 50 in the flow direction.

As described above, the shape of the corner 70 does not have any limitation as long as the shape of the corner 70 allows the flow of the fluid G flowing along the side surface 51 of the return vane 50 to change and generates the streamwise vortexes 80 downstream of the return vane 50 in the flow direction. Here, as for the shape of the corner 70 capable of easily generating a streamwise vortex 80 or generating a strong streamwise vortex 80, it is preferable that the corner 70 have an acute angle rather than an obtuse angle, and be formed of straight lines rather than curved lines.

Descriptions will be provided for operation of a centrifugal rotary machine including return vanes according to one or more embodiments of the present invention, with reference to FIGS. 1, 2, and 3A.

When a drive source of a non-illustrated motor or the like is driven, the rotating shaft 12 is rotationally driven, and the impellers 40 are rotationally driven (see FIG. 1). The fluid G taken in from the suction port 21 flows into the compression flow path 31, is given a centrifugal force by the impeller 40 rotating together with the rotating shaft 12, and is sent (pumped) radially outward.

The fluid G sent out radially outward from the compression flow path 31 flows into the diffuser flow path 32, and part of the dynamic pressure given by the impeller 40 is converted into static pressure. The fluid G the pressure of which has been increased while passing from the compression flow path 31 through the diffuser flow path 32 flows into the return flow path 33, where turning components in the flow of the fluid G are eliminated by the return vanes 50 and sent to the compression flow path 31 in the next stage (see FIGS. 1 and 2).

In this return flow path 33, the flow direction of the fluid G flowing along the side surface 51 of the return vane 50 changes such that the fluid G is swirled by the ditches 60 (grooved surfaces 61), and the streamwise vortexes 80 of the fluid G are generated downstream of the return vane 50 in the flow direction (see FIG. 3A). These streamwise vortexes 80 suppress the separation of the fluid G from the side surface 51 and breaks the transverse vortexes 90 similarly generated downstream of the return vane 50 in the flow direction.

As described above, the centrifugal compressor 1 including the return vanes 50 reduces the fluid loss at the return vanes 50 and improves the efficiency of the centrifugal compressor 1.

According to one or more embodiments of the invention, the corners 70 (ditches 60) are formed on one side surface (pressure surface) 51 of the return vane 50, where the separation of the fluid G is likely to occur, to suppress the separation of the fluid G on the side surface 51. As a matter of course, the present invention is not limited to this. For example, the corners 70 (ditches 60 or protrusions 62) may be formed on the other (opposite) side surface (pressure surface) 53 of the return vane 50 to suppress the separation of the fluid G on the side surface 53.

INDUSTRIAL APPLICABILITY

One or more embodiments of the present invention relate to stationary vanes to be provided in a fluid machine and a centrifugal compressor including the stationary vanes. One or more embodiments of the present invention reduce the fluid loss at the stationary vanes and improve the efficiency of the fluid machine. Thus, one or more embodiments of the present invention can be utilized extremely usefully for various fluid machines including stationary vanes, such as centrifugal compressors, turbochargers, and pumps.

REFERENCE SIGNS LIST

1 centrifugal compressor (fluid machine)

11 casing

11 a first side wall of casing

11 b second side wall of casing

12 rotating shaft

13 bearing

21 suction port

22 discharge port

30 flow path

31 compression flow path

32 diffuser flow path

33 return flow path

40 impeller

50 return vane (stationary vane)

50 a trailing edge of return vane (downstream edge in the flow direction)

51 side surface of return vane (suction surface)

52 rear end surface of return vane (downstream end in the flow direction)

53 side surface of return vane (pressure surface)

60 groove

61 grooved surface

70 corner

80 streamwise vortex

90 transverse vortex

W groove width (width of groove)

H groove depth (depth of groove)

T vane thickness

L groove length (length of groove)

a groove interval (distance between grooves)

C₈₀ vortex axis of streamwise vortex

C₉₀ vortex axis of transverse vortex

G fluid

Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims. 

1. A stationary vane provided to a fluid machine, the stationary vane comprising: a side surface exposed to a fluid and formed along a flow direction of the fluid; and a corner formed on the side surface, wherein the corner generates a streamwise vortex with a vortex axis extending along the flow direction of the fluid, on a downstream side in the flow direction of the fluid.
 2. The stationary vane according to claim 1, wherein the corner is formed by a ditch recessed from the side surface.
 3. The stationary vane according to claim 2, wherein a plurality of the ditches are formed on the side surface, arranged in a direction intersecting the flow direction of the fluid, and the ditches have different shapes depending on a speed of the fluid flowing along the side surface in a vicinity of each of the ditches.
 4. A centrifugal compressor including: a casing; a rotating shaft rotatably supported by the casing; an impeller provided to the rotating shaft and that is rotationally driven together with the rotating shaft; and a flow path formed in the casing and that houses the impeller, wherein the centrifugal compressor compresses a fluid by passing the fluid through the flow path, and the centrifugal compressor comprises the stationary vane according to claim 1 in the flow path.
 5. A centrifugal compressor including: a casing; a rotating shaft rotatably supported by the casing; an impeller provided to the rotating shaft and that is rotationally driven together with the rotating shaft; and a flow path formed in the casing and houses the impeller, the centrifugal compressor compresses a fluid by passing the fluid through the flow path, and the centrifugal compressor comprises the stationary vane according to claim 2 in the flow path.
 6. A centrifugal compressor including: a casing; a rotating shaft rotatably supported by the casing; an impeller provided to the rotating shaft and that is rotationally driven together with the rotating shaft; and a flow path formed in the casing and houses the impeller, the centrifugal compressor compresses a fluid by passing the fluid through the flow path, and the centrifugal compressor comprises the stationary vane according to claim 3 in the flow path. 